Abstract Background Employers are important stakeholders in efforts to facilitate the return-to-work (RTW) of employees after sick-leave, but the available data reveal large variation in employer support for RTW across European countries and firms. This paper explores in a comparative perspective what factors at the country level and at the firm level can explain these differences. Methods Employer support for RTW is examined using microdata covering 31 countries from the Third European Survey of Enterprises on New and Emerging Risks (ESENER), conducted in 2019 (N = 9,775). These data are integrated with country-level indicators to capture national differences in economic incentives and institutional provisions concerning the management of sick-leave. Two-level mixed-effects logit models with random intercepts are used to estimate the impact that different firm characteristics and country-level factors have on the propensity to provide RTW support. Results The empty model has an intraclass correlation coefficient (ICC) of 0.345, indicating that a substantial share of the observed variation across European firms is determined at the country level. Larger establishments and those with workplace health risks are more likely to provide RTW support. Including firm-level indicators does however not reduce the observed between-country variance. Institutional differences in the economic costs of sick leave for employers, on the other hand, explain about 15% of this variance. The ICC drops more strongly after including in the model policy indicators that capture activating elements in the social security system and the existence of national policies targeting RTW. The full model explains almost two thirds (62.8%) of the observed between-country variance. Conclusions The findings highlight that only in few European countries employers are systematically involved in RTW support and strengthen the case for comprehensive policy strategies to engage employers in worker activation. Key messages • Employer characteristics, such as firm size, impact the propensity to provide RTW support, but they do not explain the large between-country variation that we observe across Europe. • Comprehensive national policy strategies and institutional incentives are crucial to engage employers systematically in RTW efforts.